A small sized display panel of liquid crystal type or inorganic or organic electro-luminescence (EL) type has been produced on a large scale at a low price in recent years. The small sized display panel of this type has been used for the electronic shelf label, the electronic personal authentication card, the electronic ticket and the like. The electronic shelf label has been placed in a supermarket or a retail store to display a price of article on the display panel. This enables the price thereof to be changed promptly, when the sum of money thereof have changed many times a day because of special limited offers or special sales, by any wireless information transfer or any information transfer through wire.
The electronic personal authentication card has been used for permission card of entrance or exit of a visitor when he or she temporarily visits an office building or the like of an enterprise. This enables his or her section, guidance in a company, public relations (PR) of product of the company or the like to be displayed at need. The electronic ticket has been used for a ticket of admission of a concert or an amusement park. This enables any necessary information for a user such as a program on that day, a schedule or the like to be displayed promptly. If this is able to be collected, this may be reused on another event. Of course, such cards are driven using a battery. The following will describe a configuration of such an electronic card for these uses.
FIG. 12 is a block diagram of an information displaying device 10 according to the conventional example showing the configuration example thereof. The information displaying device 10 shown in FIG. 12 is applicable to the above-mentioned electronic cards and is configured to have a driver IC 2, a booster circuit 3, a power supply 4, CPU 5, and a display portion 12. The display portion 12 has a liquid crystal display board 101.
The power supply 4 is connected with the booster circuit 3 and the CPU 5 and the booster circuit 3 is connected with the driver IC 2. The driver IC 2 is connected with the liquid crystal display board 101 through a common electrode wiring (hereinafter, referred to as “COM wiring 13”) and a pixel electrode wiring (hereinafter, referred to as “SEG wiring 14”). The power supply 4 is a driving force for supplying electric power to the booster circuit 3 and the CPU 5.
The booster circuit 3 is a voltage-generating means for generating plural driving voltages and supplying them to the driver IC 2. The voltage-generating means fixes COM reference voltage, SEG-High voltage and SEG-Low voltage which are generated by a voltage divider that is composed of a transistor, resistance, an external electrolytic capacitor and the like and supplies them to the driver IC 2.
The CPU 5 controls input/output of the booster circuit 3 and the driver IC 2. The CPU 5 outputs a power notice signal S5 of previously set logic to the booster circuit 3. The booster circuit 3 becomes off state when the power notice signal of active state (high level) is received and becomes on state when the power notice signal of inactive state (low level) is received.
After the COM reference voltage, SEG-High voltage and SEG-Low voltage to the liquid crystal display board 101 have become off state by the CPU 5, the above-mentioned booster circuit 3 operates to discharge electric charges charged on the COM electrode and the SEG electrode, respectively, of each pixel in the liquid crystal display board 101. The driver IC 2 has an X driver 26 for COM electrode (shown as COM electrode DIV (X) in the drawing) and a Y driver 27 for SEG electrode (shown as SEG electrode DIV (Y) in the drawing).
The display portion 12 displays an image based on the X driver 26 and the Y driver 27. In the display portion 12, the COM electrode is arranged along an X direction (row direction) and the SEG electrode is arranged a Y direction (column direction), which are not shown. In the display portion 12, the COM electrode and the SEG electrode are arranged so as to be intersected.
Here, a flow of signal from the driver IC 2 to the display portion 12 will be described. The driver IC 2 shown in FIG. 12 operates to drive and display the display portion 12 by applying pixel voltages based on the display information such the an image, “ABC” is displayed on the SEG electrodes along the Y direction through the Y driver 27 and the SEG wiring 14 and by applying a scanning signal on the COM electrodes along the X direction through the X driver 26 and the COM wiring 13.
In this moment, the X driver 26 applies a bias voltage (COM voltage) constituting the scanning signal on the COM electrodes along the X direction through the COM wiring 13 and applies a bias voltage (SEG voltage) constituting the pixel signal on the SEG electrodes along the Y direction through the SEG wiring 14. When the bias voltage is applied to the COM electrode and the SEG electrode at the same time, a dot of the intersection thereof turns on a light. This enables the image, “ABC” to be displayed on the display portion 12.
Regarding such information displaying device, patent document 1 discloses a liquid crystal display driving circuit. In the liquid crystal display driving circuit, a power supply circuit, an output circuit, a booster circuit, a resistance circuit and two capacitors are provided. The resistance circuit is configured so that two resistance elements are connected in series.
An end of the power supply circuit and an end of the resistance circuit are connected with a power supply at a higher potential side. The other end of the power supply circuit is connected with an end of the booster circuit and an output of the booster circuit is connected with the output circuit. The other output of the booster circuit is connected with the power supply at a lower potential side through second capacitor. An output terminal of the output circuit is connected with a connection point between the resistance elements in the resistance circuit through a first capacitor.
The power supply circuit receives voltage supplied from an outer power supply having the power supplies with the higher potential side and the lower potential side. The booster circuit receives an output from the power supply circuit and boosts it. The output circuit receives one output of the booster circuit. The second capacitor allows the other output of the booster circuit to be connected with the lower potential side. A part of the output from the output circuit is connected with the lower potential side through the first capacitor and the resistance element. On assumption thereof, when applying an output voltage of the output circuit on the liquid crystal display, the resistance circuit switches on or off based on polarities of the output of the booster circuit. Thus configured liquid crystal display driving circuit enables to be manufactured the same configuration model (of mobile phone) without any reference to positive or negative of the voltage output of the booster circuit.
Regarding such information-displaying device, patent document 2 discloses a display power supply device and an image displaying apparatus. According to the image displaying apparatus, the display power supply device, a display controller and a display portion are provided. The display power supply device has voltage-generating means, switching means and resistance elements. To the display controller, the voltage-generating means is connected.
To an output terminal of the voltage-generating means, the display portion and an end of the switching means are connected through an output wiring. The other end of the switching means is connected to an end of the resistance element. The other end of the resistance element is connected to a lower potential side. The voltage-generating means outputs plural predetermined output voltages to the display portion based on a power supply OFF notice signal and an input voltage. The display controller outputs the power supply OFF notice signal to the voltage-generating means and the switching means. The display controller outputs a display signal to the display portion.
The display portion displays an image based on the display signal and the output voltage. On assumption thereof, the display controller controls the voltage-generating means to output the plural predetermined output voltages or stop them and controls the switching means to switch from off to on when controlling the voltage-generating means to stop them. Thus configured image display apparatus enables any residual image and latch-up after the power supply is switched off to be avoided and it enables electrical power consumption during display driving to be decreased.